An experimental investigation into wing in ground effect over flat and wavy surfaces

Abstract

The effect that wavy and flat surfaces have on the aerodynamics of aerofoils operating in Ground Effect (IGE) has been investigated.  Experiments were conducted in the Southampton University rolling road wind tunnel and the Circulating Water Channel (CWC) at QinetiQ Haslar.  Two aerofoils were tested a DHMTU 12-35.3-10.2-80.12.2 and a NACA 0012.  The DHMTU aerofoil was the primary section of interest to this research and the NACA 0012 was used as a control.  Force measurements, flow visualisation and pressure measurements were used to assess the DHMTU aerodynamic characteristics in ground effect.  The operating Reynolds Number was 830,000 and 550,000 in the wind tunnel and CWC respectively.  Wings operating at these low Reynolds Numbers are applicable to a novel small Unmanned Wing In Ground Effect Vehicle (UWIGV) describe in this thesis.

Analysis of data obtained in the rolling road wind tunnel showed that the overall drag of both the DHMTU and NACA 0012 aerofoils is greater in ground effect than out of ground effect.  A significant reduction in the vortex drag of both aerofoils is produced as a result of flying in ground effect.  Unfortunately the significant reduction in vortex drag coupled with the increase in the zero lift drag is not sufficient enough to reduce the overall drag of the trail sections in ground effect.  As the altitude of both the aerofoils decreases the lift increases.  This showed that the increase in aerodynamic efficiency as a result of flying IGE is due to the increase in lift.

Analysis of simulated flight over wavy surfaces in the CWC shows that as a wing flies over a wavy surface the lift varies from a maximum to a minimum. The amplitude of the lift force oscillation increases with decreasing altitude.  A general result is that as the wavelength of the surface decreases the maximum lift experienced by the wing decreases and the minimum lift increases.  The drag on the wing over a wavy surface in ground effect varies with altitude and as a function of wing position over the wavelength.  Like lift it varies between a minimum and maximum value.  The positions over the wavy surfaces where minimum and maximum drag was recorded are identical to the extremes of lift.

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